You know the nature of bitcoin mining is that because of the difficulty increases you will slowly be mining less and less unless you keep buying hardware to keep up.

There have been two difficulty increases in the past few weeks of 4.9% and 13.5% https://bitcoinwisdom.com/bitcoin/difficulty

The other thing that can affect how much you get paid out regularly is the luck of the pool.

Ah, ok. Well that explains it. It still feels like the difficulty jumped higher than that though. So the difficulty spike applies to mining the btc blockchain in general or just Slushpool's mining pool?